The present invention relates to a device for measuring feed movement of the type comprising a measuring scale and a scanning unit for scanning the scale.
Path measuring systems of the type conceived generally as length measuring systems are known to the art. One type of such path measuring system includes an incrementally graduated scale which is housed within an extruded aluminum housing. See, for example, West German DE-OS No. 27 12 421. In this prior art system a scanning unit is provided for scanning or reading the measuring scale, and the scanning unit is mounted within an aluminum housing. A follower which defines a cross-sectional shape of a two-edged sword is mounted to the scanning unit and is brought out of the aluminum housing through a longitudinal slit defined in the aluminum housing. The free end of this follower outside of the housing can be fastened to one of two machine components, the relative movement of which is to be measured. For example, such systems can be used to measure relative movement between the bed and slide piece of a machine tool.
In addition, it is known to the art that feed movements of machine components can be measured in systems in which the feed movements are brought about, for example by the movement of a piston in a cylinder. For example, compressed air cylinders can be used to move pistons without piston rods to provide the desired machine feed motion, and the change in position of the piston within the cylinder can be measured as an index of the machine feed motion. In the event a standrd measuring system such as that disclosed in DE-OS No. 27 12 412 is used to measure the feed movement of a piston without a piston rod in a compressed air cylinder, the overall size of the total apparatus is nearly double that of the compressed air cylinder alone.